Theories of learning state that habit formation occurs when the control of actions depends on preceding stimuli (stimulus-response or SR) rather than the action's outcome (response-outcome or RO). Understanding the mechanisms underlying habit formation may have implications for studies on drug addiction, which occurs when drug administration becomes habitual. We propose to examine the neuronal mechanisms in prefrontal cortex (PFC) that underlie these two types of control. We will focus on the encoding of this information in working memory, given the extensive literature implicating prefrontal mechanisms in this process. We will record neuronal activity from single neurons in awake behaving monkeys trained to hold action contingencies in working memory. Our specific aims are as follows: 1. To test whether neurons in medial PFC encode RO contingencies in working memory relative to neurons in lateral PFC. 2. To test whether neurons in medial PFC encode RO contingencies, while neurons in orbital PFC encode stimulus-outcome contingencies. 3. To examine whether overlearning decreases the encoding of RO contingencies relative to SR contingencies. SIGNIFICANCE: Understanding the neural mechanisms underlying action control at single neuron level has the potential to highlight novel treatments for illnesses involving dysfunctional behavioral control. This includes addictive behavior, such as drug abuse, as well as other forms of compulsive behavior. PUBLIC HEALTH RELEVANCE: Addicts initially take drugs because of their pleasurable effects, but soon their drug-taking becomes a habit. The mere sight or memory of items associated with drug-taking can cause the addict to go looking for more drugs. By determining the brain mechanisms that underlie this change in behavior we hope to discover new therapeutic strategies to break bad habits and drug addiction.